This invention relates generally to electrical fuses, and, more particularly to fuses including enclosed fuse elements for opening electrical circuits during low overcurrent conditions.
Fuses are widely used as overcurrent protection devices to prevent costly damage to electrical circuits. Fuse terminals typically form an electrical connection between an electrical power source and an electrical component or a combination of components arranged in an electrical circuit. One or more fusible links or elements, or a fuse element assembly, is connected between the fuse terminals so that when electrical current through the fuse exceeds a predetermined limit, the fusible elements melt and open one or more circuits through the fuses to prevent electrical component damage.
A fuse element or assembly is enclosed in a nonconductive housing or body extending between the terminals. Typically, the fuse body includes a substantially uniform bore of generally constant cross sectional area therethrough. When the fuse element or assembly is inserted into the bore of the fuse body during assembly of the fuse, the fuse element may be non-centered with respect to the bore, or in other words too close to a portion of the fuse body. As current flows through the fuse element or assembly, the portion of the fuse body closest to the fuse element may draw heat from the fuse element that would otherwise contribute to opening of the fuse element. While this effect is negligible at high overcurrent values that generate large amounts of heat, heat loss to the fuse body can significantly impair operational reliability of fuse elements designed to open in relatively low overcurrent conditions that generate relatively small amounts of heat. This is particularly the case when the warmest portions of the fuse element touch a portion of the fuse body after assembly of the fuse.
Some conventional fuses therefore employ mechanisms to properly position the fuse element within a fuse body. For example, in one type of fuse, washers are utilized at each end of a fuse body to prevent a fuse element from touching sidewalls of the fuse body. In another type of fuse, the fuse element is inserted through an opening in a fuse termination and soldered to the termination to correctly position the fuse element within a fuse body when the termination is attached to the body. In still another type of known fuse, a bridge is employed within a fuse body to support a fuse element and to prevent the fuse element from contacting the interior of the fuse body
While the above-described constructions have achieved success in isolating a fuse element from an interior of a fuse body, proper positioning of the fuse element within the body is achieved only with additional components that require additional assembly steps and material costs.
In an exemplary embodiment, a fuse body includes a first end, a second end and a bore extending therethrough for receiving a fuse element or fuse element assembly. The bore includes a clearing portion having a first cross sectional area and a positioning portion having a second cross sectional area. The first cross sectional area is larger than the second cross sectional area.
More specifically, in one embodiment, a substantially circular bore extends through a substantially rectangular fuse body. The clearing portion extends for a first length, and the positioning portion extends for a second length that is less than the first length. A guide portion is located intermediate the clearing portion and the positioning portion, and includes a cross sectional area intermediate, or in between, the cross sectional areas of the positioning portion and the clearing portion to facilitate insertion of the fuse element assembly into the fuse body bore.
The positioning portion provides a receptacle for receiving the fuse element assembly and ensuring that the fuse element is substantially centered within the clearance portion, thereby creating a clearance between the warmest portions of the fuse element assembly and the fuse body that may impair operation of the fuse element assembly in an overcurrent condition. As such, the warmest portions of the fuse element are prevented from touching the interior of fuse body bore. Reliable fuse operation is therefore ensured even for very low fault currents.